Method of controlling endoscope and endoscope

ABSTRACT

An endoscope  100  includes a first light source  45  that emits white illumination light, a second light source  47  that emits narrow-band light and an imaging section that has an imaging device  21  having plural detection pixels and images a region to be observed. The imaging section is caused to output a captured image signal including both a return light component of the white illumination light from the region to be observed by and a return light component of the narrow-band light the white illumination light. From the captured image signal, the return light component of the narrow-band light is selectively extracted, and a brightness level of the extracted return light component of the narrow-band light is changed by changing a light amount of light emitted from the second light source  47.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2009-219241 (filed Sep. 24, 2009), No. 2010-146866 (filed Jun. 28,2010), and No. 2010-163443 (filed Jul. 20, 2010), the entire contents ofwhich are hereby incorporated by reference, the same as if set forth atlength.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method of controlling an endoscopeand an endoscope.

2. Description of the Related Art

Recently, an endoscope is used which applies narrow-band light in aspecific narrow wavelength band to biological mucosa tissue to obtaintissue information at a desired depth of the body tissue, i.e., performa so-called special light observation (see JP 2002-34893 A(corresponding to US 2003/0176768 A, US 2008/0281154 A and US2008/0294105 A))). In such an endoscope, it is possible to easilyvisualize body information, which cannot be obtained in a normalobservation image, such as microstructure of a new blood vesselgenerated in a mucosa layer or submucosa layer and enhancement of alesion part. For example, for a cancer lesion part that is an object tobe observed, when blue narrow-band light is applied to the mucosatissue, it is possible to observe micro blood vessels or microstructureof superficial layer more specifically. Therefore, it is possible todiagnose the lesion part more exactly.

However, in the special light observation, the observation is performedwith a captured image that is obtained when the narrow-band light isapplied to the body tissue. Hence, even when an intensity ofillumination of the narrow-band light is appropriately adjusted at theobservation time in a closeup view, it is not possible to obtain anintensity of illumination enough to observe the superficial bloodvessels at the observation time in a distant view having a wide angle ofview. Due to this, a gain of an imaging section or a display section isadjusted whenever observation conditions such as an observation objector an observation position is changed, thereby enabling the observationto be performed with a proper brightness level. Additionally, in theendoscope of JP 2002-34893 A, the light from a white light source ischanged in a time division manner by a color filter, and light (R light,G light, B light) in different wavelength bands are frame-sequentiallyemitted to perform an imaging. Due to this, in order to obtain anobservation image of full colors in real time, it is necessary tocombined captured images of plural frames (R frame, G frame, B frame),so that it is difficult to increase a frame rate of the observationimage.

SUMMARY OF THE INVENTION

One embodiment of the invention provides a method of controlling anendoscope that always generates an observation image by narrow-bandlight having a proper brightness level even when observation conditionssuch as observation object and an observation position are changed inperforming a special light observation by an endoscope and that enablesbody information obtained by the narrow-band light to be clearlyobserved, and an endoscope.

One embodiment of the invention has the following configuration.

(1) A method controls an amount of illumination light of an endoscope.The endoscope includes a first light source, a second light source andan imaging section. The first light source emits white illuminationlight. The second light source that emits narrow-band light having awavelength band narrower than that of the white illumination light. Theimaging section images a region to be observed by an imaging devicehaving a plurality of detection pixels. The method includes: causing theimaging section to output a captured image signal including both of areturn light component of the white illumination light from the regionto be observed and a return light component of the narrow-band lightfrom the region to be observed; and selectively extracting the returnlight component of the narrow-band light from the captured image signal;and changing an amount of the narrow-band light emitted from the secondlight source to change a brightness level of the extracted return lightcomponent of the narrow-band light.(2) An endoscope includes a first light source, a second light source,an imaging section and a controller. The first light source emits whiteillumination light. The second light source emits narrow-band light of awavelength band narrower than the white illumination light. The imagingsection includes an imaging device having a plurality of detectionpixels. The imaging section outputs a captured image signal. Thecontroller changes an amount of light emitted from the second lightsource, based on the control method of (1).

With the above method of controlling the endoscope, even if theobservation conditions such as an observation object and an observationposition are changed in performing the special light observation withthe endoscope, it is possible to always generate an observation image bythe narrow-band light having a proper brightness level and to clearlyobserve the body information obtained by the narrow-band light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating an exemplary embodiment of the inventionand is a conceptual block diagram of an endoscope.

FIG. 2 is an appearance view of an example of the endoscope shown inFIG. 1.

FIG. 3 is a graph showing spectra of purple laser light from a purplelaser light source and blue laser light from a blue laser light sourceand emission spectrum which is obtained by wavelength-converting theblue laser light by a fluorescent material.

FIG. 4 schematically shows blood vessels in mucosal surface of bodytissue.

FIG. 5 is a schematic example of an observation image that is displayedby an endoscope and is an explanatory view showing a white lightobservation image and a narrow-band light observation image.

FIG. 6 is a flow chart showing a sequence of controlling a brightnesslevel of an image signal when images are captured with a whiteillumination light source and a special light source.

FIG. 7A illustrates an example of captured image data.

FIG. 7B illustrates the image data which is divided into image areas.

FIG. 7C illustrates a weighting process which is executed according toscreen positions.

FIG. 7D illustrates corrected image data which has been subjected to theweighting-process.

FIG. 8A illustrates characteristic image areas which are extracted fromthe image data.

FIG. 8B illustrates emphasized image data.

FIG. 8C illustrates the captured images after brightness levels thereofare adjusted.

FIG. 8D illustrates an image which is adjusted to have a targetbrightness level.

FIG. 9 shows another example of emission spectra of illumination lightby a white illumination light source, a special light source and afluorescent material.

FIG. 10 is a flow chart showing alternative sequences of S6 and S7 inFIG. 6.

FIG. 11 shows a schematic structure of another endoscope in which awhite light source is modified.

FIG. 12 shows a schematic structure of further another endoscope using awhite light source and a laser light source.

DETAILED DESCRIPTIONS OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of the invention will be specificallydescribed with reference to the accompanying drawings.

FIG. 1 is a view illustrating an exemplary embodiment of the inventionand is a conceptual block diagram of an endoscope. FIG. 2 is anappearance view of an example of the endoscope shown in FIG. 1.

As shown in FIGS. 1 and 2, an endoscope 100 includes an endoscope 11, acontrol apparatus 13 to which the endoscope 11 is connected, a displaysection 15 that is connected to the control apparatus 13 and displaysimage information, and an input section 17 that receives an inputoperation. The endoscope 11 is an electronic endoscope having anillumination optical system that emits illumination light from a leadingend of an endoscope insertion part 19, which is inserted into an objectto be examined, and an imaging optical system including an imagingdevice 21 (see FIG. 1) that has detection pixels of plural colors andcaptures a region to be observed.

The endoscope 11 has the endoscope insertion part 19, an operationsection 23 (see FIG. 2) that performs a bending operation of the leadingend of the endoscope insertion part 19 and an observation operation, andconnector sections 25A, 25B enabling the endoscope 11 to be detachablyconnected to the control apparatus 13. Although not shown, variouschannels such as a forceps channel for inserting a treatment tool forcollecting tissue and an air supply/water supply channel are provided inthe operation section 23 and the endoscope insertion part 19.

The endoscope insertion part 19 has a flexible part 31 havingflexibility, a bending part 33 and a leading end part (hereinafter,referred to as endoscope leading end part) 35. As shown in FIG. 1, theendoscope leading end part 35 has irradiation ports 37A, 37B throughwhich light is applied to a region to be observed, and an imaging device21 that obtains image information of the region to be observed, such asCCD (Charge Coupled Device) type image sensor or CMOS (ComplementaryMetal-Oxide Semiconductor) type image sensor. In addition, in front of alight-receiving surface of the imaging device 21, an object lens unit 39is arranged. When a CCD type image sensor is used, it is possible toobtain a captured image having low noise and less image distortionbecause of the global shutter of the CCD sensor.

The bending part 33 is provided between the flexible part 31 and theleading end part 35, and can be bent by a rotation operation of an angleknob 22 disposed in the operation section 23 shown in FIG. 2. Thebending part 33 can be bent in arbitrary direction and arbitrary angle,depending on parts of an object to be examined for which the endoscope11 is used, thereby enabling observation directions of the irradiationports 37A, 37B and imaging device 21 of the endoscope leading end part35 to be directed toward a desired observation part. In addition,although not shown, the irradiation ports 37A, 37B of the endoscopeinsertion part 19 are provided with a cover glass or lens.

The control apparatus 13 has a light source device 41 that generatesillumination light to be supplied to the irradiation ports 37A, 37B ofthe endoscope leading end part 35, and a processor 43 that executesimage processing for a captured image signal from the imaging device 21.The control apparatus 13 is connected to the endoscope 11 via theconnector sections 25A, 25B. In addition, the processor 43 is connectedwith the display section 15 and the input section 17. The processor 43executes the image processing for the captured image signal transmittedfrom the endoscope 11, based on a command from the operation section 23or input section 17 of the endoscope 11, and generates and suppliesimages to the display section 15 for display.

The light source device 41 has a blue laser light source (whiteillumination light source) 45 having a center wavelength of 445 nm and apurple laser light source (special light source) 47 having a centerwavelength of 405 nm, as light emitting sources. The light emitted fromthe semiconductor light emitting devices of the respective light sources45, 47 are individually controlled by a light source control section 49,so that a light amount ratio of the light emitted from the blue laserlight source 45 and the light emitted from the purple laser light source47 can be changed.

Examples of the blue laser light source 45 and the purple laser lightsource 47 include InGaN-based laser diodes of a broad area type.Alternatively, InGaNAs-based diodes or GaNAs-based diodes may be alsoused. Additionally, a light emitting element such as light emittingdiode may be used for the light sources.

The laser light emitted from the respective light sources 45, 47 arerespectively input to optical fibers by condenser lenses (not shown) andare transmitted to the connector section 25A via a combiner 51, which isan optical multiplexer, and a coupler 53, which is an opticaldemultiplexer. It is noted that the invention is not limited thereto.For example, the laser light from the respective light sources 45, 47may be directly transmitted to the connector section 25A without usingthe combiner 51 and the coupler 53.

The laser light, which are transmitted to the connector section 25Aafter the blue laser light having the center wavelength of 445 nm andthe purple laser light source having the center wavelength of 405 nm arecombined, are transmitted to the endoscope leading end part 35 of theendoscope 11 by optical fibers 55A, 55B, respectively. The blue laserlight excites fluorescent materials 57, which are an example ofwavelength conversion members disposed at light emitting ends of theoptical fibers 55A, 55B of the endoscope leading end part 35, therebyemitting fluorescence. In addition, a part of the blue laser lightpasses through the fluorescent materials 57, as it is. The purple laserlight passes through the fluorescent materials 57 without exciting thefluorescent materials 57, so that it becomes illumination light of anarrow-band wavelength.

The optical fibers 55A, 55B are multimode fibers. As the fibers, a thinfiber cable having a core diameter of 105 μm, a clad diameter of 125 μmand a diameter φ of 0.3 to 0.5 mm, which includes a protective layerthat is an outer cover, may be used, for example.

The fluorescent materials 57 include plural fluorescent materials (forexample, YAG-based fluorescent materials or fluorescent materials of BAM(BaMgAl₁₀O₁₇)) that absorb a part of the blue laser light to excitedlyemit light of green to yellow. Thereby, the light of green to yellow,which are obtained by the excitation light of the blue laser light, andthe blue laser light, which passes through the fluorescent materials 57without being absorbed by the fluorescent materials 57, are combined toconstitute white (pseudo-white) illumination light. As this exemplaryembodiment, when the semiconductor light emitting devices are used asthe excitation light sources, it is possible to obtain the white lightof high intensity in a high light emitting efficiency, to easily adjustan intensity of the white light and to suppress changes in colortemperatures and chromaticity of the white light.

The fluorescent materials 57 can prevent noise superposition, which isan obstacle to the imaging, or flicker that is generated when displayinga moving picture, which are caused due to speckles generated bycoherence of the laser lights. In addition, the fluorescent material 57is preferably made of material in which light of an infrared region islittle absorbed and highly scattered, taking into consideration adifference of refractive indices between a fluorescent substanceconstituting the fluorescent material and a resin for fixing andsolidification becoming a filler. Thereby, it is possible to increase ascattering effect without decreasing the intensity of light of red orinfrared region, so that an optical loss is reduced.

FIG. 3 is a graph showing spectra of the purple laser light from thepurple laser light source 47 and blue laser light from the blue laserlight source 45 and emission spectrum which is obtained bywavelength-converting the blue laser light by the fluorescent materials57. The purple laser light is indicated with an emission line having acenter wavelength of 405 nm (profile A). Also, the blue laser light isindicated with an emission line having a center wavelength of 445 nm.The excited emission light from the fluorescent materials 57 by the bluelaser light forms a spectral intensity distribution in whichluminescence intensity is increased in a wavelength band of about 450 nmto 700 nm. The white light is formed by the profile B of the excitedemission light and blue laser light.

The white light described in the specification is not strictly limitedto the light including all wavelength components of the visible lights.For example, the white light may include light of specific wavelengthbands such as R (red), G (green) and B (blue) that are reference colors.For example, the white light may include light including wavelengthcomponents from green to red or light including wavelength componentsfrom blue to green, in a broad sense.

In the endoscope 100, it is possible to relatively increase or decreasethe luminescence intensities of the profiles A and B by the light sourcecontrol section 49 and to thus generate illumination light having anybrightness balance.

Referring to FIG. 1, as described above, the illumination lightincluding the white light, which is formed by the blue laser light andthe excited emission light from the fluorescent materials 57, and thenarrow-band light by the purple laser light is applied toward a regionto be observed of an object to be examined from the leading end part 35of the endoscope 11. An image of the region to be observed to which theillumination light is applied is formed on the light receiving surfaceof the imaging device 21 by the object lens unit 39 and captured.

A captured image signal output from the imaging device 21 after theimaging is transmitted to an A/D converter 65 through a scope cable 63,which is then converted into a digital signal. The converted signal isinput to an image processing section 67 of the processor 43 through theconnector section 25B. The image processing section 67 converts theinput digital image signal to image data and outputs, to a controlsection 73, desired output image information and a control signal forthe light source control section 49, in cooperation with an imageanalysis section 69 and a light amount control signal generation section71, which will be specifically described below.

The output image information which is input to the control section 73 isdisplayed on the display section 15 as an endoscope observation image,and is stored in a storage section 75 having a memory or a storagedevice, if necessary. In addition, the endoscope 11 includes a modeswitching button 77 which will be described in detail below, and aswitching signal from the mode switching button 77 is input to thecontrol section 73.

FIG. 4 schematically shows blood vessels in mucosal surface of bodytissue. The mucosal surface of body tissue is reported in whichcapillary vessels B2 such as dendritic vascular network are formed toextend from blood vessels B1 of deep mucosa to the mucosal surface, andit has been reported that the lesions of the body tissue are exhibitedin the microstructure of the capillary vessels B2. Accordingly, whenperforming an endoscope diagnosis, it is attempted to find a microlesion in early stage or to diagnose a range of lesions by emphasizingan image of the capillary vessels of the mucosal surface with thenarrow-band light of visible short wavelengths of blue to purple.

When the illumination light is incident into the body tissue, theillumination light is diffusively spread in the body tissue. Theabsorption and scattering properties of the body tissue depends onwavelengths, and the scattering property is stronger as the wavelengthis shorter. In other words, a degree of light reaching a deep positionis changed depending on the wavelengths of the illumination light. Whenthe illumination light is in a wavelength band λa of about 400 nm, theblood vessel information is obtained from the capillary vessels in themucosal surface. When the illumination light is in a wavelength band λbof about 500 nm, the blood vessel information including blood vessels inthe deeper layer is obtained. Due to this, when the blood vessels in thebody tissue is observed, a light source having a center wavelength of360 to 800 nm, preferably 365 to 515 nm is used. In particular, when thesuperficial blood vessels are observed, a light source having a centerwavelength of 360 to 470 nm, preferably 360 to 450 nm is used.

FIG. 5 is an example of an observation image by the endoscope. For awhite light observation image which is obtained when the white light isused as the illumination light, a blood vessel image of the relativelydeep mucosa is obtained, and the brightness of the entire image can beeasily enhanced. In the meantime, for a narrow-band light observationimage which is obtained when the narrow-band light including manyvisible short wavelength components is used as the illumination light,it is possible to clearly see the micro capillary vessels in the mucosalsurface.

If the observation image by the white light and the observation image bythe narrow-band light are combined, it is possible to secure thesufficient brightness for the entire image and to obtain an observationimage in which the capillary vessels in the mucosal surface of the bodytissue are enhanced and an affected area can be thus easily diagnosed.Accordingly, in the endoscope 100 of this exemplary embodiment, thenarrow-band light of the profile A and the white light of the profile Bshown in FIG. 3 are individually emitted from the endoscope leading endpart 35 and the amount of the light thereof is continuously controlled.Also, the amount of the light is controlled so that the light componentsof the both illumination light are included in one frame of the imagingframes by the imaging device 21. In other words, a captured image, whichis obtained by imaging a region to be observed to which both the whitelight and the narrow-band light are applied in an arbitrary light amountratio, becomes an observation image.

By independently controlling the amount of the white light and theamount of the narrow-band light, it is possible to emphasize or bluronly the imaging information by the narrow-band light in the observationimage and to generate an observation image. Thus, the observation imagesby the both light are appropriately combined without the observationimage by the narrow-band light being hidden by the observation image bythe white light. Thereby, it is possible to obtain an observation imagesuitable for an endoscope diagnosis, which enables the micro bloodvessel structure to be easily examined by emphasizing the superficialblood vessels by the narrow-band light, while brightly illuminating theentire surrounding of the observation part with the white light.

Next, based on a flow chart of FIG. 6, it will be described a sequenceof controlling a ratio of the amount of light emitted from the bluelaser light source 45 which is a white illumination light source and theamount of the purple laser light source 47 which is a special lightsource so as to properly maintain an average brightness of the entirecaptured image and a mixing balance of the image by the narrow-bandlight and the image by the white light, when performing the imaging withthe illumination light in which the white light is added to thenarrow-band light.

First, in a state where both the blue laser light source 45 and thepurple laser light source 47 shown in FIG. 1 are turned on to apply thenarrow-band light and the white light to a region to be observed, theregion to be observed is imaged by the imaging device 21. A resultantlyobtained captured image signal is input to the image processing section67, so that each captured image (R, B) having a predetermined toneexpression width as shown in FIG. 7A is obtained (S1). The respectivecaptured images (R, G, B) constitute image information which is obtainedat the same imaging timing.

When the imaging device 21 is an imaging device of a primary colorsystem, detection levels of R, G and B that are detection colors aretreated as brightness values of the reference colors (R, G, B). However,when the imaging device is an imaging device of a complementary colorsystem, detection levels of three colors of C (cyan), M (magenta) and Y(yellow) which are detection colors or four colors of C, M, Y and Gwhich are detection colors are calculated and converted into brightnessvalues of the reference colors of R, G and B.

In the meantime, the conversion of CMY or CMYG into RGB is performed bythe image processing section 67, based on a predetermined calculationequation or table. In other words, the captured images (C, M, Y) orcaptured image (C, M, Y, G) which has been subjected to the A/Dconversion are converted into signals of captured images (R, G, B) ofthe respective reference colors. The blue component of the shortestwavelength of the captures images (R, G, B) of the respective referencecolors includes information of the superficial blood vessels B2 (seeFIG. 4), which is obtained by the narrow-band light having the centerwavelength of 405 nm.

The image processing section 67 divides the captured images (R, G, B) ofthe respective reference colors into arbitrary number of image areasMij, as shown in FIG. 7B (S2). In the shown example, the captured images(R, G, B) are commonly divided into 16 (4×4) image areas in total (Mij:I=0 to 3, j=0 to 3). In the meantime, the division number of the imageareas may be arbitrary.

Next, with regard to the respective divided captured images (R, G, B),the image analysis section 69 performs a weighting process for eachimage area Mij to obtain corrected image data Rc, Gc, Bc (S3). As shownin FIG. 7C, the weighting process is a process of emphasizing image areaPA in a screen center of each captured images (R, G, B), compared to animage area PB of a screen surrounding, particularly a process ofemphasizing an observation object displayed on the screen center to becarefully watched. The brightness value of each captured image iscorrected by a matrix calculation using a correction matrix. In thecorrected image data (Rc, Gc, Bc) in which the screen centers of thecaptured images (R, G, B) are weighted, the information of the capillaryvessels B2 of the superficial layer, which is a main observation object,is emphasized, as shown in FIG. 7D.

Next, the image analysis section 69 calculates a reference brightnessvalue A that indicates brightness of the entire image of the correctedimage data (Rc, Gc, Bc) (S4). The reference brightness value A is anindex obtained by averaging the brightness values of respective pixelsof the corrected image data (Rc, Gc, Bc) for all pixels (N pixels), asshown in an equation (1).

$\begin{matrix}{A = \frac{{\sum\limits_{N}{Rc}} + {\sum\limits_{N}{Gc}} + {\sum\limits_{N}{Bc}}}{3N}} & (1)\end{matrix}$

The control section 73 changes the light amount of the whiteillumination light so that the reference brightness value A obtainedfrom the corrected image data (Rc, Gc, Bc) approaches a predeterminedtarget brightness level TL1 (S5). In other words, the image processingsection 67 compares the reference brightness value A, which is obtainedby the image analysis section 69, with the target brightness level TL,which is stored in the storage section 75 in advance, and causes thelight amount control signal generation section 71 to generate a controlsignal to increase or decrease (change) the light amount of the lightemitted from the blue laser light source 47 so that the referencebrightness value A approaches the target brightness level TL.

The generated control signal is transmitted to the light source controlsection 49 via the control section 73, and the light source controlsection 49 controls the light amount of light emitted from the bluelaser light source 47, based on the input control signal. Thereby, whenthe reference brightness value A is less than the target brightnesslevel TL, the light amount of the white illumination light is increased,and when the reference brightness value A exceeds the target brightnesslevel TL, the light amount of the white illumination light is decreased.

Next, the image processing section 67 calculates integrated brightnessvalues GSij, BSij of the respective pixels in the respective dividedimage areas Mij of the captured images (G, B) obtained in S1 (S6). Inother words, the image processing section calculates the integratedbrightness values GSij, BSij for each of the total of 16 image areas Mijof the captured images (G, B).

Then, the image processing section calculates a brightness ratio α,which is a ratio of the integrated brightness value GSij to theintegrated brightness value BSij, in the image areas Mij having a samerelation in image position to each other, based on an equation (2). Theimage processing section 67 extracts an image area(s) having thebrightness ratio α which greater than a reference brightness ratio αc,which is a predetermined threshold value, as a characteristic image areaMC(k).

$\begin{matrix}{\alpha = \frac{{GS}_{i,j}}{{BS}_{i,j}}} & (2)\end{matrix}$

FIG. 8A shows the characteristic images areas MC(k) extracted from thecaptured images (B, G) (for example, three image areas: k=1, 2, 3).

Next, for the captured image (B) including much information about thecapillary vessels B in the superficial layer emphasized by thenarrow-band light having the center wavelength of 405 nm, the imageprocessing section 67 emphasizes the respective pixels of the extractedcharacteristic image areas MC(k) by the weighting process, therebyobtaining blue emphasized image data (Be) as shown in FIG. 8B (S8). Theemphasized image data (Be) is an image obtained by emphasizing thecharacteristic image areas MC(k) only. In the shown example, the imageareas in which the capillary vessels B are displayed are emphasized sothat its brightness is greater than the other image areas.

Then, the image processing section 67 calculates integrated brightnessvalue BeS for the entire screen, based on an equation (3).

$\begin{matrix}{{BeS} = {\sum\limits_{N}{Be}}} & (3)\end{matrix}$

Here, the control section 73 causes the light amount control signalgeneration section 71 to generate a control signal to increases ordecreases (change) the light amount of light emitted from the purplelaser light source 47, so that the obtained integrated brightness valueBeS approaches a predetermined target characteristic image brightnesslevel TLc. The control signal is input to the light source controlsection 47 through the control section 73. Then, when the integratedbrightness value BeS is less than the target characteristic imagebrightness level TLc, the light source control section 49 increases thelight amount of light emitted from the purple laser light source 47, andwhen the integrated brightness value BeS exceeds the targetcharacteristic image brightness level TLc, the light source controlsection decreases the light amount of light emitted from the purplelaser light source 47 (S10).

After the light amount of light emitted from the purple laser lightsource 47 is adjusted, a captured image signal is obtained by theimaging device 21, so that respective captured images (Ra, Ga, Ba) aregenerated (S11). Then, the reference brightness value A of the capturedimages (Ra, Ga, Ba) is calculated by the weighting process for eachimage area and the equation (1). An example of the captured images (Ra,Ga, Ba) is shown in FIG. 8C. If the reference brightness value A exceedsthe target brightness level TL, for example, if the brightness level ofthe captured image exceeds a maximum tone expression width as a resultof the adjustment of the amount of the emitted light, it is necessary tocorrect. Therefore, if the reference brightness value A exceeds thetarget brightness level TL, the amounts of light emitted from the bluelaser light source 45 and the purple laser light source 47 are decreasedin a same ratio so that the reference brightness value A becomes thetarget brightness level TL (S12).

Thereby, as shown in FIG. 8D, an observation image is obtained in whichboth the image information by the white light and the image informationby the narrow-band light, which is controlled to have a desiredbrightness level, are made to have proper brightness levels for theentire screen.

As described above, the imaging is performed by emitting the narrow-bandlight and the white light at the same time, so that it is possible toemphasize and display the superficial blood vessels by the narrow-bandlight while securing the brightness of the observation image by thewhite light. In other words, the imaging is performed by emitting thelight from both the white illumination light source for normalobservation and the special light source for special observation. As aresult, the obtained observation image becomes an image in which anobject (for example, superficial blood vessels and glands), which isintended to be observed by the narrow-band light, is made to have anoptimal brightness level and the brightness value is not saturated forthe entire image, i.e., the maximum tone expression width is notexceeded. Thereby, it is possible to always display an observationobject having a proper brightness level and to clearly display anobservation part, which is emphasized by the narrow-band light, withoutbeing hidden by the white light. Accordingly, it is possible to easilyobtain an endoscope observation image, which can contribute to an earlyfinding of a lesion part, without an operator's adjustment operation.

With the observation image, it is possible to observe a detailedstructure of the superficial layer emphasized by the narrow-band lightin real time while seeing the entire structure of the observation partby the white illumination light. Hence, by increasing a trackingproperty to movement of an observation object at a high frame rate, withregard to the cancer lesion in which a density of the micro bloodvessels is increased compared to a normal part, for example, it ispossible to diagnose the superficial micro blood vessels ormicrostructure quickly and accurately while comparing them with thesurroundings of the lesion part.

In the meantime, although the blue laser light source 45 and the purplelaser light source 47 are turned on at the same time to perform theimaging, it may be possible to alternately turn on the light sources 45and 47 within a light receiving time period in one frame of the imagingdevice. In this case, it is possible to save the power and suppress theheat generation.

Also, the brightness level control of the captured image signal isswitched between ON and OFF by pushing the mode switching button 77 (seeFIG. 1). In the case of the ON state, the special light observation modeis made effective, so that it is possible to perform the observation bythe white light illumination and the narrow-band light at the same time.In the case of the OFF state, the normal observation mode is madeeffective, so that it is possible to change the light amount of lightemitted from the purple laser light source 47 in the same ratio as thelight amount of light emitted from the blue laser light source 45. Inthis manner, it is possible to improve the usability of the endoscope byselectively switching between the special light observation mode and thenormal observation mode.

Furthermore, the observation object by the narrow-band light may beautofluorescence or drug fluorescence from the body tissue, in additionto the superficial capillary vessels or micro mucosa shape of the bodytissue. Also, the intensity of the return light from the region to beobserved may be appropriately changed into a state suitable fordiagnosis.

FIG. 9 shows another example of emission spectra of illumination lightby the white illumination light source, the special light source and thefluorescent material. As shown, depending on types of the fluorescentmaterials, the fluorescent material is excited by not only the bluelaser light having the wavelength of 445 nm but also the purple laserlight having the wavelength of 405 nm. In this case, when the lightamount of the purple laser light having the wavelength of 405 nm isincreased, the state that the entire observation image is bluish can bemitigated by the excitation light of the fluorescent material caused bythe purple laser light, so that it is possible to suppress the change incolor balance of the white illumination. In the meantime, an excitationlight emission amount of the fluorescent material by the purple laserlight is set to be one-several-th (at least ⅓, preferably ⅕, morepreferably 1/10 or less) of an excitation light emission amount by theblue laser light. In this manner, by suppressing the excited emissionlight of the fluorescent material by the purple laser light, it ispossible to perform the special light observation while properly keepingthe color temperature of the white illumination.

In the meantime, the extraction of the characteristic image area MC(k)may be performed as follows. That is, the characteristic image area(s)MC(k) are extracted by comparing the brightness values of the capturedimages (B, G) in divided image area units of the captured images (B, G).However, when comparing the brightness values of the captured images (B,G) in pixel units of each captured image, it is possible to extract anobject to be emphasized by the narrow-band light more accurately. Morespecifically, as shown in FIG. 10 illustrating alternative sequences ofS6 and S7 of FIG. 6, a ratio of a brightness value of the captured image(B), which includes much information of reflection light of thenarrow-band light having the center wavelength of 405 nm, to abrightness value of the captured image (G) at the same pixel position iscalculated, and a characteristic pixel(s) in which the ratio is equal toor greater than a predetermined ratio are extracted (S6A).

As shown in FIG. 7B, the captured image (B) and the captured image (G)are commonly divided into the image areas Mij, and the number ofextracted characteristic pixels is calculated for each of the imageareas Mij. Then, an image area(s) in which the number of characteristicpixels is equal to or greater than a predetermined threshold value areextracted as the characteristic image area(s) MC(k) (S7A).

In this manner, by comparing the brightness values of the capturedimages (B, G) in pixel units at the same pixel positions, it is possibleto extract the body information, which is obtained by the narrow-bandlight, more certainly.

Next, another exemplary embodiment of the endoscope will be described.

FIG. 11 shows a schematic structure of another endoscope in which thewhite light source is modified. In the structure shown in FIG. 11, as awhite light source 81, a light source, which emits light of a broadwavelength band, such as a halogen lamp, a xenon lamp or a white lightemitting diode, is used to emit the white illumination light from theleading end of the endoscope 11 through a light guide 83 that is anoptical fiber bundle. The light emitted from the special-light lightsource 47 is transmitted to the leading end of the endoscope 11 throughthe connector section 25A by the optical fiber 55B, as described above.Then, the light is provided as narrow-band light from a lightdeflection/diffusion member 85 that is disposed at a light emitting endof the optical fiber 55B. In the meantime, the lightdeflection/diffusion member 85 may be replaced with a light irradiationwindow that is disposed at the leading end of the endoscope 11.

With the above structure, it is possible to introduce the whiteillumination light having high color rendering properties and having abroad spectrum characteristic with a simple structure. Furthermore, itis possible to suppress the heat generation of the leading end of theendoscope. In addition, since it is possible to completely separate andemit the white illumination light and the narrow-band light, it ispossible to emit the narrow-band light to a region to be observedwithout a fluorescent material. Therefore, it is possible to remove theunnecessary light emission from the fluorescent material, so that it ispossible to easily control the light amount.

FIG. 12 shows a schematic structure of further another endoscope inwhich the structure of the special light source is modified. In FIG. 12,the optical system of the white illumination light is omitted, and anystructure shown in FIG. 1 or FIG. 11 may be used. The special lightsource of this structure generates the narrow-band light by (i) a whitelight source 47A, which emits light of a broad wavelength band such as ahalogen lamp, a xenon lamp or a white light emitting diode, in place ofthe purple laser light source 47 emitting the narrow-band light, and(ii) optical filter 111. The transmitted light from the optical filter111 is introduced into a light incident end of a light guide 112 by alight collection member 113 and is guided to the leading end of theendoscope 11 by the light guide 112.

The optical filter 111 is a narrow band-pass filter that allows only apredetermined narrow-band wavelength component of incident white lightto pass therethrough and is formed in a part of a rotation filter plate115. The rotation filter plate 115 can switch among the optical filters111, which are disposed in the middle of a light path of the whitelight, through rotation driving by a motor M. That is, plural opticalfilters 111, 117, 119 (the number of optical filters is not limited tothree) are disposed in the middle of the light path so as to be switchedand thus, so that the narrow-band lights of different types can beemitted.

With the above structure, it is possible to simply generate anynarrow-band light from the white light source.

The invention is not limited to the above exemplary embodiments. Inother words, the exemplary embodiments can be changed and/or modified byone skilled in the art based on the specification and the well-knowntechnology, which are within the scope of the invention to be protected.

As described above, one embodiment of the invention discloses thefollowing matters.

(1) A method controls an amount of illumination light of an endoscope.The endoscope includes a first light source, a second light source andan imaging section. The first light source emits white illuminationlight. The second light source that emits narrow-band light having awavelength band narrower than that of the white illumination light. Theimaging section images a region to be observed by an imaging devicehaving a plurality of detection pixels. The method includes: causing theimaging section to output a captured image signal including both of areturn light component of the white illumination light from the regionto be observed and a return light component of the narrow-band lightfrom the region to be observed; and selectively extracting the returnlight component of the narrow-band light from the captured image signal;and changing an amount of the narrow-band light emitted from the secondlight source to change a brightness level of the extracted return lightcomponent of the narrow-band light.

With the method of controlling the endoscope, when observation isperformed using the white illumination light from the first light sourceand the narrow-band light from the second light source as theillumination light, it is possible to always obtain the observationinformation by the narrow-band light having the proper brightness leveleven when the observation conditions such as an observation object andan observation position are changed. Thereby, the information obtainedby the narrow-band light can be clearly observed without being hidden bythe white illumination light.

(2) In the method of (1), a center wavelength of the narrow-band lightemitted from the second light source may be in a range of 360 nm to 470nm.

With the method of controlling the endoscope, the center wavelength ofthe second light source is within the range of 360 nm to 470 nm.Therefore, it is possible to clearly detect the image informationindicating the superficial blood vessels or microstructure of the bodytissue, particularly.

(3) The method of any one of (1) to (2) may further include: generatingcaptured images of plural reference colors based on the captured imagesignal, wherein the captured images include a first captured image and asecond captured image, and of the captured images, the first capturedimage contains the most return light component of the narrow-band lightemitted from the second light source; and dividing the first capturedimage and the second captured image, which has a different referencecolor from that of the first captured image, into common plural imageareas; integrating brightness values in each image area of the firstcaptured image to calculate an integrated brightness value of each imagearea of the first captured image; integrating brightness values in eachimage area of the second captured image to calculate an integratedbrightness value of each image area of the second captured image;obtaining a ratio of (i) the integrated brightness value of each imagearea of the first captured image and (ii) the integrated brightnessvalue of the image area, having a same image positional relationshipwith each image area of the first captured image, of the second capturedimage; extracting image areas, of the first and second captured images,whose ratio is equal to or larger than a threshold value, ascharacteristic image areas; and changing the amount of light emittedfrom the second light source while adopting a brightness level of theextracted characteristic image area of the first captured image as abrightness level of the return light component of the narrow-band lightfrom the region to be observed.

With the method of controlling the endoscope, among the image areasobtained by dividing the captured images, the emission light amount ofthe second light source is changed so that the return light component ofthe narrow-band light has a desired brightness level in thecharacteristic image area in which a ratio of the integrated brightnessvalues of the different reference colors is equal to or greater than thepredetermined threshold value. Thereby, it is possible to particularlyemphasize and observe the body information in the image areas where thebody information obtained by the narrow-band light is much included.

(4) The method of any one of (1) to (2) may further include: generatingcaptured images of plural reference colors based on the captured imagesignal, wherein the captured images include a first captured image and asecond captured image, and of the captured images, the first capturedimage contains the most return light component of the narrow-band lightemitted from the second light source; and dividing the first capturedimage and the second captured image, which has a different referencecolor from that of the first captured image, into common plural imageareas; obtaining a ratio of (i) a brightness value of each image pixelof the first captured image and (ii) a brightness value of a pixel,having a same image positional relationship with each pixel of the firstcaptured image, of the second captured image; extracting pixels, of thefirst and second captured images, whose ratio is equal to or larger thana threshold value, as characteristic pixels; obtaining the number ofcharacteristic pixels in each image area of the first and secondcaptured images; extracting image areas, of the first and secondcaptured images, whose number of characteristic pixels is equal to orlarger than a threshold value, as characteristic image areas; andchanging the amount of light emitted from the second light source whileadopting a brightness level of the extracted characteristic image areaof the first captured image as a brightness level of the return lightcomponent of the narrow-band light from the region to be observed.

With the method of controlling the endoscope, the characteristic pixelswhose ratio of the brightness values of the different reference colorsat the same pixel position is equal to or greater than the predeterminedratio are extracted. Among the image areas obtained by dividing thecaptured images, the emission light amount of the second light sourceunit is changed so that the light receiving component of the narrow-bandlight has a desired brightness level in the characteristic image areawhere the number of the characteristic pixels is equal to or greaterthan the predetermined threshold value. Thereby, it is possible toparticularly emphasize and observe the body information in the imagearea in which the body information obtained by the narrow-band light ismuch included.

(5) In the method of any one of (1) to (4), if the return lightcomponent of the white illumination light from the region to be observedand the return light component of the narrow-band light from the regionto be observed exceed a predetermined target brightness level after theamount of light emitted from the second light source is changed, theamount of light emitted from the first light source and the amount oflight emitted from the second light source may be decreased.

With the method of controlling the endoscope, even when the brightnesslevel of the return light components exceeds the target brightness levelafter the emission light amount of the second light source is changed,it is possible to correct the return light to have a proper brightnesslevel without changing the balance of the lights emitted from the firstlight source and the second light source.

(6) In The method of any one of (3) to (5), light components of colorsdetected by the imaging device may include light components of a primarycolor system of blue, green and red. The reference color of the firstcaptured image may be blue. The reference color of the second capturedimage may be green.

With the method of controlling the endoscope, it is possible to observethe body information obtained by the irradiation of the narrow-bandlight of the blue wavelength, more clearly from the detection result ofthe reference color light of the primary color system.

(7) In the method of any one of (3) to (5), light components of colordetected by the imaging device may include light components of acomplementary color system including magenta, cyan and yellow. The lightcomponents of the detected colors may be converted into light componentsof a primary color system of blue, green and red. The reference color ofthe first captured image may be the converted blue. The reference colorof the second captured image may be the converted green.

With the method of controlling the endoscope, it is possible to observethe body information obtained by the irradiation of the narrow-bandlight of the blue wavelength, more clearly from the detection result ofthe reference color light of the complementary color system.

(8) A method of controlling an endoscope includes switching between (i)a special light observation mode in which the method of any one of (1)to (7) is performed, and (ii) a normal observation mode in whichbrightness levels of the plural captured images are changed at a sameratio.

With the method of controlling the endoscope, the special lightobservation mode and the normal observation mode can be selectivelyswitched, so that the usability of the endoscope can be improved.

(9) An endoscope includes a first light source, a second light source,an imaging section and a controller. The first light source emits whiteillumination light. The second light source emits narrow-band light of awavelength band narrower than the white illumination light. The imagingsection includes an imaging device having a plurality of detectionpixels. The imaging section outputs a captured image signal. Thecontroller changes an amount of light emitted from the second lightsource, based on the control method of any one of (1) to (8).

With the endoscope, when the observation is performed using theillumination light having the white light added to the narrow-bandlight, it is possible to always obtain the observation information bythe narrow-band light having the proper brightness level even when theobservation conditions such as an observation object and an observationposition are changed. Thereby, the information obtained by thenarrow-band light can be clearly observed without being hidden by thewhite illumination light.

(10) In the endoscope of (9), the first light source may include afluorescent material, and a semiconductor light emitting device thatemits excitation light of the fluorescent material.

With the endoscope, the white illumination light is formed by lightemitted from the semiconductor light emitting device and the excitationemission light from the fluorescent material by the light emission.Therefore, the white light having a high intensity is obtained in a highlight emission efficiency, and the intensity of the white light can beeasily adjusted. Also, the semiconductor light emitting device is used,so that the change in color temperature and chromaticity of the whitelight can be suppressed.

(11) In the endoscope of (9), the first light source may emit lightwhich originates from a xenon light source or a halogen light source.

With the endoscope, the white light of a broad spectrum is obtained fromthe xenon light source or halogen light source, so that it is possibleto improve the color rendering properties.

(12) In the endoscope of any one of (9) to (11), the second light sourcemay include a semiconductor light emitting device.

With the endoscope, the semiconductor light emitting device is used toemit the narrow-band light of high efficiency and high intensity.

(13) In the endoscope of any one of (9) to (11), the second light sourcemay generate the narrow-band light by having light originating from axenon light source or a halogen light source pass through a narrow-bandpass filter which only allows to pass light having predeterminednarrow-band wavelength components therethrough. The second light sourcemay emit the generated narrow-band light.

With the endoscope, it is possible to simply generate desirednarrow-band light by the narrow band-pass filter.

What is claimed is:
 1. A method of controlling an endoscope comprising afirst light source section that emits white illumination light, a secondlight source section that emits narrow-band light having a wavelengthband narrower than that of the white illumination light, and an imagingsection that captures a region to be observed by an imaging devicecomprising detection pixels of plural colors, the method comprising:causing the imaging section to output a captured image signal includinga return light component of the white illumination light from the regionto be observed and a return light component of the narrow-band lightfrom the region to be observed, wherein the captured image signalcomprises a red image signal, a green image signal, and a blue imagesignal; generating captured images of red, green, and blue colors basedon the red, green, and blue image signals, respectively, wherein thecaptured images include a first captured image, and of the capturedimages, the first captured image contains a most return light componentof the narrow-band light emitted from the second light source; changinga brightness level of the first captured image relatively to brightnesslevels of captured images based on the red and green signals; dividingthe first captured image and a second captured image which has adifferent reference color from that of the first captured image intocommon plural image areas; integrating brightness values in each imagearea of the first captured image to obtain an integrated brightnessvalue of each image area of the first captured image; integratingbrightness values in each image area of the second captured image toobtain an integrated brightness value of each image area of the secondcaptured image; obtaining a ratio of the integrated brightness value ofeach image area of the first captured image and the integratedbrightness value of the image area, having a same image positionalrelationship with each image area of the first captured image, of thesecond captured image; extracting image areas, of the first and secondcaptured images, whose ratio is equal to or larger than a thresholdvalue, as characteristic image areas; and selectively changing abrightness level of the characteristic image area of the first capturedimage.
 2. The method according to claim 1, wherein a center wavelengthof the narrow-band light emitted from the second light source is in arange of 360 nm to 470 nm.
 3. The method according to claim 1, whereinthe changing of the brightness level includes changing a correctionmatrix which is used to correct brightness values of respective pixelsin the captured image signal by a matrix operation, the method furthercomprising: correcting a captured image signal, which is newly obtainedfrom the imaging section, using the changed correction matrix.
 4. Themethod according to claim 3, further comprising: if a brightness levelof an image obtained by correcting the captured image signal, which isnewly obtained from the imaging section, using the changed correctionmatrix exceeds a predetermined target brightness level, resetting thecorrection matrix so as to decrease the brightness level of thecorrected image.
 5. The method according to claim 1, wherein lightcomponents of detection colors which are detected by the imaging deviceinclude light components of a primary color system containing blue,green and red, wherein the reference color of the first captured imagecomprises blue, and wherein the reference color of the second capturedimage comprises green.
 6. The method according to claim 1, wherein lightcomponents of detection colors which are detected by the imaging deviceinclude light components of a complementary color system containingmagenta, cyan, and yellow, wherein the light components of therespective detection colors are converted into light components of aprimary color system of blue, green and red, wherein the reference colorof the first captured image comprises blue, and wherein the referencecolor of the second captured image comprises green.
 7. The methodaccording to claim 1, wherein the imaging device includes a CCD-type(Charge Coupled Device type) image sensor.
 8. The method according toclaim 1, wherein the imaging device includes a CCD-type (Charge CoupledDevice type) image sensor, and wherein the brightness level of the firstcaptured image is changed by changing an amplification ratio of anamplifier of each pixel of the imaging device.
 9. A method ofcontrolling an endoscope, said method comprising: switching between: aspecial light observation mode in which the method according to claim 1is performed; and a normal observation mode in which brightness levelsof the plural captured images are changed at a same ratio.
 10. A methodof controlling an endoscope comprising a first light source section thatemits white illumination light, a second light source section that emitsnarrow-band light having a wavelength band narrower than that of thewhite illumination light, and an imaging section that captures a regionto be observed by an imaging device comprising detection pixels ofplural colors, the method comprising: causing the imaging section tooutput a captured image signal including a return light component of thewhite illumination light from the region to be observed and a returnlight component of the narrow-band light from the region to be observed,wherein the captured image signal comprises a red image signal, a greenimage signal, and a blue image signal; generating captured images ofred, green, and blue colors based on the red, green, and blue imagesignals, respectively, wherein the captured images include a firstcaptured image, and of the captured images, the first captured imagecontains a most return light component of the narrow-band light emittedfrom the second light source; changing a brightness level of the firstcaptured image relatively to brightness levels of captured images basedon the red and green signals; dividing the first captured image and asecond captured image which has a different reference color from that ofthe first captured image into common plural image areas; obtaining aratio of a brightness value of each image pixel of the first capturedimage and a brightness value of a pixel, having a same image positionalrelationship with each pixel of the first captured image, of the secondcaptured image; extracting pixels, of the first and second capturedimages, whose ratio is equal to or larger than a threshold value, ascharacteristic pixels; obtaining a number of characteristic pixels ineach image area of the first and second captured images; extractingimage areas, of the first and second captured images, whose number ofcharacteristic pixels is equal to or larger than a threshold value, ascharacteristic image areas; and selectively changing a brightness levelof the characteristic image area of the first captured image.
 11. Anendoscope, comprising: a first light source section that emits whiteillumination light; a second light source section that emits narrow-bandlight having a wavelength band narrower than that of the whiteillumination light; an imaging section that captures a region to beobserved by an imaging device having detection pixels of plural colors;and a control section, wherein the control section causes the imagingsection to output a captured image signal including a return lightcomponent of the white illumination light from the region to be observedand a return light component of the narrow-band light from the region tobe observed, wherein the captured image signal comprises a red imagesignal, a green image signal, and a blue image signal, wherein thecontrol section generates captured images of red, green, and blue colorsbased on the red, green, and blue image signals, respectively, whereinthe captured images include a first captured image, of the capturedimages, the first captured image contains a most return light componentof the narrow-band light emitted from the second light source, andwherein the control section changes a brightness level of the firstcaptured image relatively to brightness levels of captured images basedon the red and green signals; a divider for dividing the first capturedimage and a second captured image which has a different reference colorfrom that of the first captured image into common plural image areas; anintegrator for integrating brightness values in each image area of thefirst captured image to obtain an integrated brightness value of eachimage area of the first captured image, and for integrating brightnessvalues in each image area of the second captured image to obtain anintegrated brightness value of each image area of the second capturedimage; a unit for obtaining a ratio of the integrated brightness valueof each image area of the first captured image and the integratedbrightness value of the image area, having a same image positionalrelationship with each image area of the first captured image, of thesecond captured image; an extractor for extracting image areas, of thefirst and second captured images, whose ratio is equal to or larger thana threshold value, as characteristic image areas; and a selector forselectively changing a brightness level of the characteristic image areaof the first captured image.
 12. The endoscope according to claim 11,wherein the first light source section includes: a phosphor; and asemiconductor light emitting element that emits excitation light for thephosphor.
 13. The endoscope according to claim 11, wherein the firstlight source section emits light which originates from a xenon lightsource or a halogen light source.
 14. The endoscope according to claim11, wherein the second light source section includes a semiconductorlight emitting element.
 15. The endoscope according to claim 11, whereinthe second light source section generates the narrow-band light byhaving light originating from a xenon light source or a halogen lightsource pass through a narrow-band pass filter which only allows to passlight having predetermined narrow-band wavelength componentstherethrough; and wherein the second light source section emits thegenerated narrow-band light.
 16. An endoscope, comprising: a first lightsource section that emits white illumination light; a second lightsource section that emits narrow-band light having a wavelength bandnarrower than that of the white illumination light; an imaging sectionthat captures a region to be observed by an imaging device havingdetection pixels of plural colors; and a control section, wherein thecontrol section causes the imaging section to output a captured imagesignal including a return light component of the white illuminationlight from the region to be observed and a return light component of thenarrow-band light from the region to be observed, wherein the capturedimage signal comprises a red image signal, a green image signal, and ablue image signal, wherein the control section generates captured imagesof red, green, and blue colors based on the red, green, and blue imagesignals, respectively, wherein the captured images include a firstcaptured image, of the captured images, the first captured imagecontains a most return light component of the narrow-band light emittedfrom the second light source, and wherein the control section changes abrightness level of the first captured image relatively to brightnesslevels of captured images based on the red and green signals; a dividerfor dividing the first captured image and a second captured image whichhas a different reference color from that of the first captured imageinto common plural image areas; a unit for obtaining a ratio of abrightness value of each image pixel of the first captured image and abrightness value of a pixel, having a same image positional relationshipwith each pixel of the first captured image, of the second capturedimage; an extractor for extracting pixels, of the first and secondcaptured images, whose ratio is equal to or larger than a thresholdvalue, as characteristic pixels; a unit for obtaining a number ofcharacteristic pixels in each image area of the first and secondcaptured images; a unit for extracting image areas, of the first andsecond captured images, whose number of characteristic pixels is equalto or larger than a threshold value, as characteristic image areas; anda selector for selectively changing a brightness level of thecharacteristic image area of the first captured image.
 17. An endoscope,comprising: a first light source section that emits white illuminationlight; a second light source section that emits narrow-band light havinga wavelength band narrower than that of the white illumination light; animaging section that captures a region to be observed by an imagingdevice having detection pixels of plural colors; and a control section,wherein the control section causes the imaging section to output acaptured image signal including a return light component of the whiteillumination light from the region to be observed and a return lightcomponent of the narrow-band light from the region to be observed,wherein the captured image signal comprises a red image signal, a greenimage signal, and a blue image signal, wherein the control sectiongenerates captured images of red, green, and blue colors based on thered, green, and blue image signals, respectively, wherein the capturedimages include a first captured image, of the captured images, the firstcaptured image contains a most return light component of the narrow-bandlight emitted from the second light source, and wherein the controlsection changes a brightness level of the first captured imagerelatively to brightness levels of captured images based on the red andgreen signals; a divider for dividing the first captured image and asecond captured image which has a different reference color from that ofthe first captured image into common plural image areas; and anintegrator for integrating brightness values in each image area of thefirst captured image to obtain an integrated brightness value of eachimage area of the first captured image, and for integrating brightnessvalues in each image area of the second captured image to obtain anintegrated brightness value of each image area of the second capturedimage.
 18. The endoscope according to claim 17, further comprising: aunit for obtaining a ratio of the integrated brightness value of eachimage area of the first captured image and the integrated brightnessvalue of the image area, having a same image positional relationshipwith each image area of the first captured image, of the second capturedimage; and an extractor for extracting image areas, of the first andsecond captured images, whose ratio is equal to or larger than athreshold value, as characteristic image areas.